34 lines
1.3 KiB
JavaScript
34 lines
1.3 KiB
JavaScript
import startOfISOWeekYear from "../startOfISOWeekYear/index.js";
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import addWeeks from "../addWeeks/index.js";
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import requiredArgs from "../_lib/requiredArgs/index.js";
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var MILLISECONDS_IN_WEEK = 604800000;
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/**
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* @name getISOWeeksInYear
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* @category ISO Week-Numbering Year Helpers
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* @summary Get the number of weeks in an ISO week-numbering year of the given date.
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*
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* @description
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* Get the number of weeks in an ISO week-numbering year of the given date.
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*
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* ISO week-numbering year: http://en.wikipedia.org/wiki/ISO_week_date
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*
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* @param {Date|Number} date - the given date
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* @returns {Number} the number of ISO weeks in a year
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* @throws {TypeError} 1 argument required
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*
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* @example
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* // How many weeks are in ISO week-numbering year 2015?
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* const result = getISOWeeksInYear(new Date(2015, 1, 11))
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* //=> 53
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*/
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export default function getISOWeeksInYear(dirtyDate) {
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requiredArgs(1, arguments);
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var thisYear = startOfISOWeekYear(dirtyDate);
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var nextYear = startOfISOWeekYear(addWeeks(thisYear, 60));
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var diff = nextYear.valueOf() - thisYear.valueOf(); // Round the number of weeks to the nearest integer
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// because the number of milliseconds in a week is not constant
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// (e.g. it's different in the week of the daylight saving time clock shift)
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return Math.round(diff / MILLISECONDS_IN_WEEK);
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} |